(1) Field of the Invention
The invention is related to an aircraft with a fuselage that defines at least an interior region and a drive system accommodating region, said aircraft comprising the features of claim 1.
(2) Description of Related Art
A fuselage of an aircraft, and in particular of a rotary-wing aircraft, generally defines an interior region and a drive system accommodating region that is arranged inside the fuselage. The interior region usually comprises at least a cockpit and may further comprise a cabin for passengers and/or cargo. The drive system accommodating region usually accommodates one or more engines that are adapted for driving the aircraft, e.g. by providing power to an associated power distribution unit, such as a gearbox, which then provides this power to a suitable propelling unit, such as e.g. a propeller, rotor or other.
Typically, the one or more engines are embodied as air breathing propulsion engines, such as diesel engines, gas engines, gas turbines and so on, which combust a fuel/air mix for power generation. In operation, all such air breathing propulsion engines need fresh air, ideally cold air, which is mixed with fuel so that these engines perform sufficiently and satisfactorily.
However, all such air breathing propulsion engines will not only generate power in operation, but also heat that must be dissipated from the engines for preventing an overheating thereof, which is crucial for the entire aircraft performance, safety and reliability. Usually, such dissipation is conducted using air that cools oil, which in turn cools an associated engine. A corresponding heat transfer from the oil to the air is frequently conducted by means of one or more oil coolers, which are propelled mechanically by the associated engine, a gearbox or electrical engines with sufficient cooling power.
In the latter case, the gearbox and/or the electrical engines also generate heat that is usually likewise transferred to oil, which dissipates the transferred heat by an air flow through one or more suitable oil coolers. However, as space and volume is generally limited in an aircraft, the engines and oil coolers, as well as other cooling devices, air intakes and/or heating or heat dissipating surfaces are commonly positioned comparatively close to each other, so that they may nevertheless affect each other thermally.
More specifically, all aircrafts currently use oil coolers and/or other cooling devices, so that an adequate working environment must be provided for these oil coolers and/or cooling devices, wherein hot air resulting from respectively generated heat is ideally transferred to surrounding ambient air. Such hot air coming from the oil coolers and/or cooling devices may have one of the following origins, which are not necessarily implemented or provided on each aircraft:                cooling of engine oil,        the surface of a main gearbox,        cooling of main gearbox oil,        a starter/generator of an engine,        other electrical engines,        auxiliary gearboxes mounted on the engines or the main gearbox,        hydraulic pumps for actuating an underlying dynamic system (e.g. swash plate), and/or        heat exchangers of an air conditioning system.        
If hot air coming from the oil coolers and/or other cooling devices warms up the fresh air that is mixed with the fuel for combustion in the above mentioned air breathing propulsion engines, a resulting air temperature will be higher than an original air temperature of the fresh air, thereby leading to a reduced engine performance in general. This occurs mainly if the hot air is expelled in a region of the aircraft that is located upstream of corresponding fresh air intakes of the air breathing propulsion engines.
Therefore, in order to avoid such a mixing, the fresh air intakes of aircrafts that are used for engine operation, or oil cooling and/or air conditioning purposes, are ideally located upfront the aircraft and corresponding hot air emitted from the oil coolers, engines and other auxiliary devices is ideally expelled at the rear of the aircraft. Thus, reinjection can be avoided and use under pressure for amplification can be enabled. This is, however, not a simple task to fulfil due to limited space, weight, architectures, etc. of aircrafts in general.
The document US20090134276 describes an aircraft with two compartments that are separated by two distinct walls of an associated firewall arrangement, which are spaced apart from each other to form an interior air duct channel. Between these two walls, a fresh air flow is ducted for cooling at least a first one of the two walls that closes up the first compartment, which accommodates e.g. a gearbox. Consequently, the first compartment is also cooled. Furthermore, the fresh air flow is ducted via an associated air duct that passes through the second one of the two walls into a gas turbine exhaust of a turboshaft engine, both of which are arranged within the second compartment, for reducing a respective gas turbine exhaust temperature in the gas turbine exhaust. However, this firewall arrangement requires a comparatively great space for installation in an area of the aircraft, where the available space is already limited, as described above.
The document U.S. Pat. No. 4,216,924 describes an aircraft in the form of a helicopter that is provided with a low drag canopy, which comprises exhaust nozzles and vents for reducing a drag occurring in operation by increasing a respective energy of the helicopter's boundary layer. The helicopter is provided with a cooling structure that is adapted for cooling the helicopter's engines and lubricating oil thereof. However, management of any hot air flow other than the one that is generated in operation of this helicopter by the engines and/or the lubricating oil respectively corresponding oil coolers, e.g. a hot air flow generated in an unfavorable warm upfront positioned region such as the main gearbox region of the helicopter, is not described. In other words, it is not described how such a hot air flow can be ducted from the unfavorable upfront positioned region to the favorable aft region of the helicopter.
Other prior art documents have been considered. The document EP2535274 describes an airliner with a tail cone housing a pair of auxiliary power and thrust unit (APTU). The APTUs adjacently are mounted in parallel relative to one another within the tail cone section. The embodiment of FIG. 3 is provided with a firewall plate positioned between the APUs, in the form of a generally U-shaped plate structure having downwardly directed lateral edge regions. An upper frame member may be attached generally at a center of the firewall plate.
The document WO9316280 describes an airliner auxiliary power unit. An eductor comprises an annular mixer nozzle receiving a flow of high velocity gas. A housing defines a first annular plenum and a second nozzle receiving the venting air from said plenum.
The document WO03037715 describes a passive cooling system for an auxiliary power unit installation on an airliner. The system comprises an auxiliary power unit housed within a nacelle. An oil cooler is contained separately within the nacelle
Furthermore, in the above described aircrafts all corresponding aft regions are usually provided with comparatively heavy heat protection layers, which are commonly used on aircrafts to protect the aft regions against hot air flows. Moreover, such aircrafts are frequently subject to hot gas reinjections resulting from main engine exhausts and/or any secondary hot exhaust gases produced by auxiliary devices.